Babies born to mothers who smoked during pregnancy had an average systolic blood pressure (the first number in a blood pressure reading) that was 5.4 points higher than that of babies whose mothers hadn't smoked or been exposed to secondhand smoke during pregnancy.

Those findings weren't affected by the babies' birth weight, the mother's age, or whether the babies were breastfed, note the researchers. They included graduate student Caroline Geerts at the University Medical Center Utrecht in Utrecht, the Netherlands.

Whether or not the mothers smoked during pregnancy didn't affect the baby's diastolic blood pressure. That's the second number in a blood pressure reading.

It's not clear whether babies born to women who smoked during pregnancy will continue to have higher systolic blood pressure as they grow up. Follow-up studies are needed, note Geerts and colleagues.

"If our findings are true, they would indicate that maternal smoking during pregnancy has a substantial impact on systolic blood pressure in early infancy," write Geerts and colleagues.

Their study appears in the advance online edition of the journal Hypertension.